It is well known to use cheap, disposable assay devices to detect the presence and/or amount of an analyte in a sample and these assay devices in particular lend themselves for use in the home and/or at point-of-care. Such devices tend to be either lateral flow assay devices or microfluidics assay devices.
Typically, lateral flow assay devices, such as those disclosed in EP291194, are of the type in which a liquid sample is applied, directly or (more usually) indirectly, to a porous matrix, such as a nitrocellulose or paper filter. The liquid sample migrates along the porous matrix, generally mobilising a dried assay reagent or component (typically a labelled antibody such as a particulate labelled antibody) releasably immobilised on the porous matrix. Typically the labelled antibody forms a complex with the analyte of interest in the sample, which labelled complex is usually then captured in a detection region of the porous matrix, by a second antibody for the analyte of interest. Accumulation of the labelled binding reagent in the detection region or zone is therefore indicative of the presence, or extent of analyte in a liquid sample. It will be appreciated that other variants of lateral flow assays exist, in particular competition format assays in which a labelled reagent tends to be captured in the detection zone if the analyte is absent from the sample.
Detection of labelled reagent at the detection zone may be carried out visually or by means of a photodetector. Visual read, non-electronic, assay devices have the advantage of being low cost, however a problem associated with such assay devices, especially pregnancy-testing devices and/or home-use assay devices, is that they provide an assay result as a signal of variable strength, which can require a degree of interpretation. This leaves the assay result open to misinterpretation, especially where the user or reader of the assay device has a preferred assay result in mind, especially in the case of a pregnancy test, where the user may have little or no experience of using such an assay device and may be in a heightened emotional state.
As a consequence, electronic digital devices have been developed wherein the presence or amount of the labelled reagent is determined by means of a photodetector and the result of the assay displayed on e.g. an LCD display. Such digital devices have the advantage in that they provide an unambiguous result such as “YES” or “NO”, or a numerical range or value, which does not require interpretation. Such devices may be single use and therefore disposable. The assay reader reads the assay by measuring the amount of detectable substance accumulated in the detection zone, typically, but not necessarily, by measuring the reflectance from, or transmission of light through, the detection zone. The lateral flow assay test strip may be inserted into the reader before or after application of the sample, or the test strip may be an integral part of the reader.
In a microfluidics assay device, many of the same principles as used in a lateral flow assay may be employed. However, instead of the liquid sample being applied to a porous matrix, the sample is applied or fed into a conduit or channel, along which the liquid advances, usually by means of capillary action. A detection zone may be provided on an inner surface of the channel on which, for example, an immobilised binding reagent is provided. Again, the result of the assay may be determined non-electronically, by visual inspection, or by an electronic assay result reader.